The present invention relates to analog component transmission of a color video signal, and more particularly, to a synchronization signal for use therewith.
It has been suggested to transmit a color video signal through a channel, such as a VTR (video tape recorder) or a satellite transmission path, using serially transmitted time compressed analog components. Serial transmission is desirable so that only one channel is needed, thereby minimizing tape consumption, while component signals, such as Y, R-Y, B-Y, rather than a composite signal are used to eliminate crosstalk between the luminance and chrominance signals. A high frequency reference signal is also transmitted every line, for example just after a horizontal sync pulse, to allow recovery and reformatting into a standard composite color signal at the receiver or playback apparatus. This recovery and playback comprises time base correcting (TBC) and time expansion. The time base corrector has a PLL (phase locked loop) that receives the high frequency reference signal and compares it to a frequency related to a VCO (voltage controlled oscillator) frequency, said relationship being a fixed ratio. The output of the VCO is used as a clock for the line store memories and time expander. Also an axis-crossing of the high frequency reference signal is used, following detection of the horizontal sync, to provide greater precision of the line starting time. However, since in general the high frequency reference signal is not an integer multiple of the horizontal frequency, there will be a line-to-line phase change between the leading edge of the horizontal sync and the reference signal. In the presence of noise, this may lead to an ambiguity of the line starting time. Further, since all lines are not identical with respect to the sync-to-reference signal phase relationship, complex circuitry, as shown for example in U.S. Pat. No. 4,024,571, is required in the TBC to maintain this relationship constant in the TBC output signal. Also the PLL circuit will be complex due to said non-integer relationship, which in turn may cause a slow lock-up time and picture jitter.
It is therefore desirable to provide a sync signal that allows simpler circuitry.